History of the Earth Chapter 14

Formation of the Earth

Where does life come from? Spontaneous generation the belief that living things arise from nonliving things Biogenesis all living things come from other living things Redi’s experiments Spallanzani’s experiments Pasteur’s experiments

Redi’s Experiment (1626-1697) Italian physician and poet who demonstrated that the presence of maggots on rotting meat does not result from spontaneous generation but from eggs laid on the meat by flies. Pg. 279

Spallanzani’s Experiments (1729-1799) Italian naturalist whose experiments disproved that microorganisms spontaneously generated from meat broth in open flasks. Pg. 280

Pasteur’s Experiment (1822-1895) A French chemist who proved that microorganisms are carried by dust and not air. Improved on Spallanzani’s experiment Pg. 281

The First Organic Compounds Alexander Oparin’s Hypothesis, 1920’s): Thought that primitive atmosphere contained: NH3, H2, H20, and C-H compounds At high temperatures, these gases might have formed simple organic compounds like amino acids

Oparin’s Theory Con’t When the Earth cooled, the water vapor condensed into lakes and seas with the organic compounds within With the help of lightening and UV radiation, these organic compounds reacted with each other forming macromolecules essential to life.

Can that REALLY happen? Yes! According to experiments performed by Miller and Urey Products of experimental synthesis: Amino acids ATP DNA nucleotides

Attempts to Create Life Miller Experiment Spark Chamber Input Chamber Condenser Water Vapor Forms

Life began in Hydrothermal Vents Extreme conditions: high heat, acid levels, pressure, gases Sun cannot reach the bottom of the ocean Chemosynthesis- organisms making their own energy from the chemicals in their enviro. (similar to photosynthesis) Currently populated by Archae

Vents cont. Scientists have also traced the DNA of all currently living organisms back to a common ancestor extremophile that would have been found in the hydrothermal vents.

“It came from outer space!” Some scientists hypothesize that organic compounds may have come from meteoroids from space

Earth’s Age More than 4 BILLION years old! How do scientists “know” this? Radiometric dating Measurement of the decay of commonly occurring radioactive isotopes Ex) Carbon dating

Fossils The remains of ancient animals and plants Found in every continent on earth Formed from sedimentary rock Paleontology- the branch of biology that studies past forms of life (namely fossils!)

Ancient Bat Saber-Toothed Cat

The Fossil Record From the 1830s onwards, geologists noted how fossils became more complex through time. The oldest rocks contained no fossils, then came simple sea creatures, then more complex ones like fishes, then came life on land, then reptiles, then mammals, and finally humans. Clearly, there was some kind of 'progress' going on.

The First Prokaryotes About 3.5 bya the first prokaryotes, cells without a true nucleus (like bacteria), came into existence. The first cells were probably anaerobic and heterotrophic. Video

Prokaryotes cont. Resemble modern day Archaebacteria, which live in extreme environments Chemosynthesis- the conversion of carbon molecules (like CO2 or methane) into organic compounds without the use of sunlight energy is obtained from an inorganic substance like sulfur, hydrogen gas, or methane

Rise of photosynthesis and aerobic respiration Cyanobacteria- group of unicellular, autotrophic prokaryotes about 3 bya Increased the level of atmospheric oxygen

The First Eukaryotes Endosymbiosis- about 2.0 bya, a small aerobic prokaryote began to live inside a larger anaerobic prokaryote aerobic prokaryotes evolved to modern mitochondria Photosynthetic cyanobacteria evolved into chloroplasts video

Endosymbiosis: From prokaryotes to eukaryotes

Ch. 14 Notebook Quiz What does the term biogenesis mean? Explain how Redi’s experiment disproved the hypothesis that flies formed by spontaneous generation. What is the Earth’s age? How do we know this? According to Oparin, what molecules were in Earth’s early atmosphere? What process increased the level of oxygen in the atmosphere about 3 bya? Explain the theory of endosymbiosis.